Thermal treatment apparatus

ABSTRACT

The present invention is a thermal processing unit including: a heating-furnace body whose upper end has an opening; a heating unit provided on an inside wall of the heating-furnace body; a reaction container consisting of a single tube contained in the heating-furnace body; a gas-discharging-pipe connecting portion formed at an upper portion of the reaction container; and a first temperature controlling unit provided around the gas-discharging-pipe connecting portion.

This application is based upon and claims the benefits of priority fromPCT/JP02/10079, filed Sep. 27, 2002, and from prior Japanese patentapplication JP2001-342636, filed Nov. 8, 2001.

FIELD OF THE INVENTION

The present invention relates to a thermal processing unit and a thermalprocessing method which are suitable for a thermal process to an objectto be processed such as a semiconductor wafer.

DESCRIPTION OF THE RELATED ART

Conventionally, in a semiconductor manufacturing process, there is astep of depositing a thin film or an oxide film onto a surface of asemiconductor wafer as an object to be processed, or a step ofconducting a diffusion of impurities onto the surface. For these steps,a thermal processing unit such as a CVD unit, an oxide-film forming unitor a diffusion unit has been used.

In such a thermal processing unit, a plurality of wafers, which areobjects to be processed, are placed on a holding tool called a waferboat in a vertical arrangement, and then loaded in a reaction containercalled a process tube that has been heated to a high temperature. Then,a reaction gas is introduced into the reaction container, so that athermal process to the wafers is conducted.

FIG. 4 shows an example of vertical thermal processing unit that hasbeen conventionally used.

In FIG. 4, a heating-furnace body 101 is placed on a base plate 103. Aresistance heater 104 is provided on an inside surface of aheat-insulating layer of the heating-furnace body 101.

A reaction container (process tube) is provided in the heating-furnacebody 101. The reaction container is surrounded by the resistance heater104. The reaction container has a double-tube structure of an outer tube121, whose upper end is closed, and an inner tube 122 installedconcentrically to the outer tube 121. The reaction container is adaptedto keep its airtightness, in order to form a processing space forconducting a process to wafers that are objects to be processed. Theouter tube 121 and the inner tube 122 are made of, for example, quartz.

Respective lower ends of the outer tube 121 and the inner tube 122 aresupported by a tubular manifold 105 a made of stainless steel or thelike. A reaction-container lower lid 110 is provided for hermeticallysealing a lower opening of the manifold 105 a, the reaction-containerlower lid 110 being freely opened and closed.

A rotational shaft 114 is rotatably inserted at a central portion of thereaction-container lower lid 110 via a magnetic-fluid seal 115 in such amanner that the airtightness of the reaction container is maintained. Alower end of the rotational shaft 114 is connected to a rotatingmechanism of an elevating mechanism 116. An upper end of the rotationalshaft 114 is fixed to a turntable 113. A wafer boat 111(object-to-be-processed boat), which is a holding tool of objects to beprocessed, is mounted on the turntable 113 via a heat-insulatingcylinder 112. A plurality of silicon wafers W are placed on the waferboat 111 in a tier-like manner. The wafer boat 111 is made of, forexample, quartz.

One or more gas-introducing pipes 109, 109′ are horizontally arranged ata lower portion of the manifold 105 a in order to introduce a processgas for a wafer process into the inner tube 122 of the reactioncontainer. The gas-introducing pipes 109, 109′ are connected to agas-supplying source, not shown, via a mass flow controller, not shown.

A gas-discharging pipe 120 connected to a vacuum pump, not shown, isconnected to an upper portion of the manifold 105 a in such a mannerthat the process gas is discharged from a gap between the outer tube 121and the inner tube 122 to set a pressure in the reaction container at apredetermined reduced pressure.

Next, a thermal process for semiconductor wafers using the above thermalprocessing unit is explained.

The thermal process for semiconductor wafers using the above thermalprocessing unit primarily consists of a preliminary heating step of thethermal processing unit, a loading step of the wafer boat, a thermalprocessing step and a cooling step.

The preliminary heating step is a step of preliminarily heating thethermal processing unit before the silicon wafers are loaded, in orderto start the processing step immediately after the loading step of thesilicon wafers.

In the next loading step, the wafer boat on which the silicon wafers areplaced is loaded into the heating furnace.

Then, in the thermal processing step, a reaction gas is introduced intothe reaction container so that the silicon wafers undergo a thermalprocess (a predetermined process is conducted).

After the process to the silicon wafers is completed, the heating andthe supply of the reaction gas are stopped, and the reaction gas and anygenerated gas remaining in the reaction container are discharged byusing a nitrogen gas while the reaction container is cooled (coolingstep).

Herein, recently, it has been requested to enhance throughput of asemiconductor manufacturing unit, and various improvements have beenachieved.

In order to enhance throughput of a semiconductor process without havingany effect on film quality of a surface of the semiconductor wafer, thegreatest possibility is to shorten times of the preliminary heating stepand the cooling step. Then, in order to shorten the times of the steps,it is necessary to shorten the heating time and the cooling time. Forthat purpose, it is necessary to reduce thermal capacity of each memberin the heating furnace in order to achieve rapid heating and rapidcooling.

However, in the conventional thermal processing unit, since the reactioncontainer has the double-tube structure, the thermal capacity thereof islarge. Thus, the conventional thermal processing unit is not suitablefor rapid heating and rapid cooling. Thus, the conventional thermalprocessing unit can not satisfy the recent request of enhancing thethroughput of a semiconductor manufacturing unit.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a thermal processingunit suitable for rapid heating and rapid cooling in which unevenness inheating an object to be processed such as a silicon wafer is improved.

Another object of the present invention is to achieve a thermalprocessing unit and a thermal processing method using the thermalprocessing unit wherein temperature control is easy and wherein particlegeneration is effectively prevented.

This invention is a thermal processing unit comprising: aheating-furnace body whose upper end has an opening; a heating unitprovided on an inside wall of the heating-furnace body; a reactioncontainer consisting of a single tube contained in the heating-furnacebody; a gas-discharging-pipe connecting portion formed at an upperportion of the reaction container; and a first temperature controllingunit provided around the gas-discharging-pipe connecting portion.

According to the invention, since the reaction container consists of asingle tube and has a smaller thermal capacity, rapid heating and rapidcooling can be achieved. In addition, since a temperature at thegas-discharging-pipe connecting portion is controlled by the firsttemperature controlling unit, particle generation at thegas-discharging-pipe connecting portion can be effectively prevented.

Preferably, a gas-discharging pipe for discharging atmosphere in thereaction container is connected to the gas-discharging-pipe connectingportion, and a second temperature controlling unit is provided aroundthe gas-discharging pipe. In the case, preferably, the first temperaturecontrolling unit and the second temperature controlling unit are adaptedto be controlled independently.

In addition, in the case, preferably, a flange is formed at an endportion of the gas-discharging-pipe connecting portion, another flangeis formed at an end portion of the gas-discharging pipe, and the flangeat the end portion of the gas-discharging-pipe connecting portion andthe flange at the end portion of the gas-discharging pipe arehermetically connected via a sealing member. In the case, preferably, onat least one of the flange at the end portion of thegas-discharging-pipe connecting portion and the flange at the endportion of the gas-discharging pipe, a third temperature controllingunit for controlling a temperature at a connecting portion of theflanges is provided.

For example, the third temperature controlling unit has a liquid-flowingtunnel formed in the flange. Alternatively, the third temperaturecontrolling unit has a heating unit for control provided in a vicinityof the flange.

In addition, in the case, preferably, the first temperature controllingunit, the second temperature controlling unit and the third temperaturecontrolling unit are adapted to be controlled independently.

In addition, preferably, the gas-discharging-pipe connecting portion isbent. In the case, preferably, the gas-discharging-pipe connectingportion is bent at an angle of about 90 degrees.

In addition, preferably, the gas-discharging-pipe connecting portion isformed in such a manner that the gas-discharging-pipe connecting portionis integral with and extended from the reaction container.

In addition, preferably, the gas-discharging-pipe connecting portion hasa cervical portion whose diameter gradually reduces from a diameter atan upper portion of the reaction container. In the case, preferably, anassistant heating unit is provided in a vicinity of the cervical portionof the gas-discharging-pipe connecting portion.

Each of the temperature controlling units is, for example, aheat-insulating member. Alternatively, each of the temperaturecontrolling units is, for example, a resistance heater.

For example, each of the temperature controlling units has flexibility.Alternatively, each of the temperature controlling units has been formedinto a shape in advance.

In addition, the invention is a thermal processing method of an objectto be processed using a thermal processing unit, the thermal processingunit including: a heating-furnace body whose upper end has an opening; aheating unit provided on an inside wall of the heating-furnace body; areaction container consisting of a single tube contained in theheating-furnace body; a gas-discharging-pipe connecting portion formedat an upper portion of the reaction container; a first temperaturecontrolling unit provided around the gas-discharging-pipe connectingportion; and an object-to-be-processed boat arranged in the reactioncontainer, for holding an object to be processed;

-   -   the thermal processing method comprising:    -   a step of conducting a thermal process of the object to be        processed by means of the heating unit, and    -   a step of controlling a temperature of the gas-discharging-pipe        connecting portion to a temperature substantially equal to a        thermal processing temperature of the object to be processed, by        means of the first temperature controlling unit.

Alternatively, the invention is a thermal processing method of an objectto be processed using a thermal processing unit, the thermal processingunit including: a heating-furnace body whose upper end has an opening; aheating unit provided on an inside wall of the heating-furnace body; areaction container consisting of a single tube contained in theheating-furnace body; a gas-discharging-pipe connecting portion formedat an upper portion of the reaction container; an object-to-be-processedboat arranged in the reaction container, for holding an object to beprocessed; a gas-discharging pipe connected to the gas-discharging-pipeconnecting portion, for discharging atmosphere in the reactioncontainer; and a second temperature controlling unit provided around thegas-discharging pipe;

-   -   the thermal processing method comprising:    -   a step of conducting a thermal process of the object to be        processed by means of the heating unit, and    -   a step of controlling a temperature of the gas-discharging pipe        to a temperature of 150 to 300° C., by means of the second        temperature controlling unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing a thermal processing unitaccording to a first embodiment of the present invention;

FIG. 2 is an enlarged view of a main part of FIG. 1;

FIG. 3 is a schematic sectional view showing a thermal processing unitaccording to a second embodiment of the present invention; and

FIG. 4 is a schematic sectional view showing a conventional thermalprocessing unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, embodiments of the present invention will be described withreference to the attached drawings.

(First Embodiment)

FIG. 1 is a schematic sectional view showing a thermal processing unitaccording to a first embodiment of the present invention. The thermalprocessing unit of the embodiment comprises: a furnace body 1; a processtube 5 of a single-tube structure as a reaction container arranged inthe furnace body 1; a gas-discharging-pipe connecting portion 6 extendedfrom the process tube 5; and a gas-discharging pipe 7 closely connectedto an end portion of the gas-discharging-pipe connecting portion 6.

In the thermal processing unit of the embodiment, an upper end of thefurnace body 1 has an opening. The opening is covered with afurnace-body lid 2. A central portion of the furnace-body lid 2 isprovided with an opening. On the other hand, an upper end of the processtube 5 protrudes to form the gas-discharging-pipe connecting portion 6.Thus, after the process tube 5 is arranged in the furnace body 1, thegas-discharging-pipe connecting portion 6 penetrates the opening of thefurnace-body lid 2 so that the furnace body 1 is covered with thefurnace-body lid 2. Preferably, the furnace-body lid 2 is formed bycombination of a plurality of dividable members.

A resistance heater (heating unit) 4 is installed inside a wall surfaceof the furnace body 1. The furnace body 1 is placed on a base plate 3.By means of the resistance heater 4, the furnace body 1 is heated toabout 300 to 1100° C., whose temperature may be different betweenthermal processes.

The process tube 5 is a single-tube type of reaction container, made ofceramics such as quartz glass or silicon carbide. A lower end of theprocess tube 5 has an opening. A manifold 5 a made of stainless steal orthe like is connected to the opening. At least one reaction-gasintroducing pipes 9, 9′ are inserted through a lateral wall of themanifold 5 a. A reaction gas for a wafer process is adapted to besupplied from the reaction-gas introducing pipes 9, 9′. Areaction-container lower lid 10 is hermetically connected to a lower endof the manifold 5 a via an O-ring, not shown.

An object-to-be-processed boat 11 made of quartz, horizontally holding aplurality of wafers W at regular intervals in a vertical direction, isarranged in the process tube 5. The object-to-be-processed boat 11 isarranged on a heat-insulating cylinder 12 in order to prevent heatdissipation from a lower portion of the object-to-be-processed boat 11.The heat-insulating cylinder 12 is placed on a turntable 13 that cancause the object-to-be-processed boat 11 to freely rotate. The turntable13 is connected to a rotational shaft 14. The rotational shaft 14penetrates an opening provided at a central portion of thereaction-container lower lid 10 and is rotatably supported by anelevating mechanism 16 while airtightness is maintained by amagnetic-fluid seal 15. The elevating mechanism 16 is adapted to supportthe object-to-be-processed boat 11 in such a manner that theobject-to-be-processed boat 11 is movable in a vertical direction.

The gas-discharging-pipe connecting portion 6, whose diameter is smallerthan a maximum diameter of a main body of the process tube 5, is formedin such a manner that the gas-discharging-pipe connecting portion 6 isintegral with and extended from the process tube 5. Thegas-discharging-pipe connecting portion 6 penetrates the opening of thefurnace-body lid 2 to protrude outside the furnace body 1.

The protruding part from the furnace-body lid 2 of thegas-discharging-pipe connecting portion 6 is located outside an areathat may be heated by the heating unit. Thus, a temperature at theprotruding part tends to fall. Because of that, as shown in FIG. 2, avertical-part first temperature controlling unit 8 a is arranged arounda vertical part of the gas-discharging-pipe connecting portion 6, and ahorizontal-part first temperature controlling unit 8 b is arrangedaround a horizontal part of the gas-discharging-pipe connecting portion6. Thus, the periphery of the gas-discharging-pipe connecting portion 6can be heated or heat-retained in order not to generate a greatdifference between a temperature around the gas-discharging-pipeconnecting portion 6 and a temperature of the main body of the processtube 5 as a reaction container.

The reason that the temperature controlling units are arranged aroundthe gas-discharging-pipe connecting portion 6 is as follows. That is,when an exhaust gas such as a reaction gas and/or a generated gasreaches the gas-discharging-pipe connecting portion 6 during a processin the thermal processing furnace, if a temperature of thegas-discharging-pipe connecting portion 6 is relatively low, the exhaustgas may be deposited at the gas-discharging-pipe connecting portion 6,so that an impurity film may be formed in the gas-discharging-pipeconnecting portion 6. If the undesired film grows, it gradually becomeseasier for the film to peel off. When the film peels off, the filmbecomes particles, which may contaminate the silicon wafers on theobject-to-be-processed boat 11 arranged in the process tube 5. Foravoiding the above problems, the first temperature controlling units 8a, 8 b are provided around the gas-discharging-pipe connecting portion 6in order for the temperature of the gas-discharging-pipe connectingportion 6 not to fall too much with respect to the temperature of themain body of the process tube 5. Thus, generation of the undesireddeposit can be prevented.

A heat-insulating material or a resistance heater may be used as thefirst temperature controlling units 8 a, 8 b arranged in the vicinity ofthe gas-discharging-pipe connecting portion 6. In particular, it ispreferable that a resistance heater is used as the first temperaturecontrolling units in order to enhance the effect of heat-retaining.

In addition, the temperature of the gas-discharging-pipe connectingportion 6 is preferably equal to a wafer process temperature (processingtemperature). Thus, uniformity of temperatures of the wafers arranged inan upper portion of the process tube 5 can be remarkably improved. Inaddition, in the case, the number of dummy wafers, which are generallyarranged on the uppermost stages of the wafer boat 11 for the uniformityof temperatures of the wafers, can be reduced. Thus, the height of theheating unit may be reduced.

The vertical-part first temperature controlling unit 8 a and thehorizontal-part first temperature controlling unit 8 b may be integralwith each other.

Preferably, the resistance heater is a heater made of a carbon wireincluding fewer impurities. In addition, the heater may be a flexibleheater that can be wound around the gas-discharging-pipe connectingportion 6 with a complicated shape, or may be a heater that has beenformed in advance into a shape to be fitted with the shape of thegas-discharging-pipe connecting portion 6.

As the flexible heater, a carbon wire may be used, the carbon wireincluding: a wire-like heater-main-body formed by braiding a pluralityof carbon fibers; and metal terminals attached to both ends of theheater-main-body. Such a flexible heater may be installed by windingaround the gas-discharging-pipe connecting portion 6 of the upperportion of the process tube 5.

Alternatively, as the previously-shaped heater, a seal heater may beused, the seal heater being formed by forming the above carbon wire intoa predetermined shape, sandwiching the carbon wire between two quartzglass plates, and heating the two quartz glass plates to melt them andfix them to the carbon wire in a predetermined shape. The seal heatermade of quartz glass has only very low possibility of impuritiescontamination, which is suitable for the present invention.

In any case, in order to avoid impurities contamination, it ispreferable to design the unit in such a manner that a temperaturecontrolling unit may be easily arranged in the unit.

As shown in FIG. 1, it is preferable that the gas-discharging-pipeconnecting portion 6 is bent at an angle of about 90 degrees toward alateral direction of the process tube 5. If a temperature of aconnecting portion of the gas-discharging-pipe connecting portion 6 andthe gas-discharging pipe 7 is lower than that of the main body of theprocess tube 5, the reaction gas and/or the generated gas remaining inthe exhaust gas are cooled to be solidified in that portion, so thatimpurity films may be formed in that portion. Then, the impurity filmsmay be peel off to generate particles. Thus, if the connecting portionis located just above the object-to-be-processed boat, the particlesgenerated in the connecting portion may fall directly on theobject-to-be-processed boat, which may cause contamination of thesilicon wafers. Therefore, it is preferable that thegas-discharging-pipe connecting portion 6 is bent, in order for theparticles not to fall directly on the object-to-be-processed boat, evenif the particles are generated in the connecting portion of thegas-discharging-pipe connecting portion 6 and the gas-discharging pipe7.

In addition, as the gas-discharging-pipe connecting portion 6 is bent,radiation heat from the resistance heater 4 that heats the process tube5 doesn't directly reach a flange 17 a formed at an end portion of thegas-discharging-pipe connecting portion 6, a flange 17 b formed at anend portion of the gas-discharging pipe 7, and the gas-discharging pipe7. Thus, temperature controls for their members are easy. In that view,preferably, the end portion of the gas-discharging-pipe connectingportion 6 is extended nearly to an extension line of the lateral surfaceof the main body of the process tube 5.

As shown in FIG. 2, the flange 17 a formed at the end portion of thegas-discharging-pipe connecting portion 6 is closely and hermeticallyfixed to the flange 17 b formed at the gas-discharging pipe 7, via anO-ring 18 made of an elastomer such as a fluorine resin.

A heat-resistant temperature of the O-ring 18 (elastomer) is usuallyabout 300° C. Thus, if the O-ring 18 is heated to a high temperature,the quality of the O-ring 18 may be deteriorated, that is, the sealingperformance may be deteriorated. In order to prevent the deteriorationof the sealing performance, it is necessary to control a temperature ofa portion close to the O-ring 18. In the embodiment, a fluid way 19 fortemperature control is formed at the flange 17 b, and a fluid fortemperature control, such as cooling water, flows through the fluid way19. Thus, the temperature of the flange 17 b is adapted to be controlledsuitably. In addition, as shown in FIG. 2, if a resistance heater (thirdtemperature controlling unit) 8 c is arranged along a side wall of theflange 17 b of the gas-discharging pipe 7, the temperature distributioncan be controlled more accurately.

The gas-discharging pipe 7 connected to the end portion of thegas-discharging-pipe connecting portion 6 is connected to a suction unitsuch as a vacuum pump, not shown. Thus, a vacuum can be created in theprocess tube 5, and the remaining reaction gas, the generated gas andthe like can be discharged from the process tube.

In the embodiment, a second temperature controlling unit 8 d is arrangedaround the gas-discharging pipe 7. Thus, more accurate temperaturecontrol can be achieved. An electric heater is preferably used as thesecond temperature controlling unit 8 d, because the control of theelectric heater is easy. It is preferable that the temperature of thegas-discharging pipe 7 is controlled within a range of 150 to 300° C.More preferable temperature of the gas-discharging pipe 7 is 200° C. Bymeans of the above temperature control, even if the exhaust (discharged)gas from the process tube 5 passes through the gas-discharging pipe 7,it can be prevented that any impurity film is generated as anunnecessary deposit in the gas-discharging pipe 7.

The exhaust gas discharged from the gas-discharging pipe 7 is cooled bya trap, not shown, which is connected to the gas-discharging pipe 7 andhas cooling fins or the like. Thus, the exhaust gas (remaining reactiongas, generated gas or the like) discharged from the process tube 5 maybe solidified and trapped thereby. It is preferable that the trap isarranged between a flange (not shown) at the other end of thegas-discharging pipe 7 and a vacuum pump (not shown) connected to thegas-discharging pipe 7.

As described above, according to the thermal processing unit of theembodiment, the temperatures of the respective members are positivelycontrolled by means of: the first temperature controlling units 8 a, 8 bfor controlling the temperature of the gas-discharging-pipe connectingportion 6; the fluid-flowing tunnel for temperature control (thirdtemperature controlling unit) 19 buried in the flange 17 b of thegas-discharging pipe 7; the resistance heater (third temperaturecontrolling unit) 8 c arranged for the side-wall portion of the flange17 b of the gas-discharging pipe 7; and the second temperaturecontrolling unit 8 d arranged along the gas-discharging pipe 7. Thus, inthe vicinities of these members, it can be effectively prevented that animpurity film as an unnecessary deposit is generated and that particlesare generated from the impurity film.

In addition, in order to improve the accuracy of temperature control, itis preferable to arrange a temperature detecting unit such as atemperature sensor at a necessary portion of each member, to conduct atemperature control by using a detected temperature. In a simple way,the temperature control may be conducted in accordance with atemperature-control sequence that has been set in advance.

(Second Embodiment)

Next, a second embodiment according to the invention is explained. Inthe second embodiment, arrangements of the heating unit for the reactioncontainer and the temperature controlling units are optimized,uniformity of thermal processing temperature within the surface of asubstrate such as a wafer is improved, and generation of defect of thesubstrate caused by ununiform heating is prevented.

The thermal processing unit of the second embodiment is shown in FIG. 3.In FIG. 3, the same elements as in FIG. 1 are accompanied with the samenumeral references, and the explanation thereof is omitted.

With reference to FIG. 3, the gas-discharging-pipe connecting portion 6is formed upward from an upper portion of the process tube 5 by reducingthe diameter of the process tube 5. A spiral heater 23 is arranged at acervical portion of the gas-discharging-pipe connecting portion 6, thatis, a portion represented by a numeral reference 25 in FIG. 3. Terminals24 of the spiral heater 23 hermetically protrude outside the furnacebody 1. Thus, the spiral heater 23 may be heated by electric powersupplied from a controller, not shown.

A plurality of spiral heaters 23 are uniformly arranged around thecervical portion 25 of the gas-discharging-pipe connecting portion 6, sothat the plurality of spiral heaters 23 are adapted to heat portionsclose to the center of an object to be processed W located on theuppermost stage of the wafer boat 11 uniformly (symmetrically withrespect to the center of the object to be processed W). The uppersurface of the substrate W located on the uppermost stage of the waferboat 11 is opposite to the gas-discharging-pipe connecting portion 6,that is, opposite to a way for discharging the atmospheric gas in theprocess tube 5. In addition, the uppermost stage of the wafer boat 11 isthe furthest from linear heaters 4 a extending in a vertical directionas a heating unit for the reaction container, so that the temperature ofthe uppermost stage tends to fall the most. However, as the spiralheaters 23 are arranged to heat the portions close to the center of theobject to be processed W located on the uppermost stage of the waferboat 11, ununiformity of temperature within the surface of the object tobe processed can be solved.

For example, each spiral heater 23 consists of: a tubular member made ofa material having electrical-insulating properties and heat-resistingproperties, such as quartz, and formed into a tubular shape; and acarbon wire heater arranged in the tubular member. The material forthose is not limited to quartz, but may be another material havingequivalent functions.

It is preferable that four spiral heaters 23 are arranged around thecervical portion 25 of the gas-discharging-pipe connecting portion 6. Inaddition, at least one of the spiral heaters 23 is preferably movable.In the case, assembling and disassembling operations of the thermalprocessing unit have no drawback.

In addition, in FIG. 3, the linear wire 4 a is a heating unit forheating the object to be processed W from an outside of the process tube5, and is a linear heater wherein the carbon wire is protected(surrounded) by the quartz tube. In the first embodiment shown in FIG.1, the heater is arranged in a spiral or circular manner so as tosurround the process tube 5. However, in the second embodiment, thelinear heater 4 a is arranged to extend in an axial direction of theprocess tube 5. The above heater 4 a has a small thermal capacity, andthus is superior in dynamic temperature characteristics. That is, theheater 4 a can be rapidly heated and rapidly cooled. In addition, theheater 4 a can be easily controlled. In the embodiment, a plurality oflinear heaters 4 a are arranged so as to surround the process tube 5.

In addition, as shown in FIG. 3, one or more upper-portion heaters 28may be arranged in an upper portion of the process tube 5. In addition,one or more lower-portion spiral heaters 26 may be arranged in a lowerportion of the process tube 5 in order to heat the objects to beprocessed W located in a lower portion of the waver boat 11.

If the upper-portion heaters 28 are arranged, heating uniformity at theupper portion of the process tube may be improved.

If the lower-portion heaters 26 are arranged, heat dissipation from theobjects to be processed W arranged in the lower portion of the waferboat 11 through the lower end of the process tube 5 may be prevented.

Preferably, each of the upper-portion heaters 28 and the lower-portionheaters 26 consists of a carbon wire heater contained in a quartz tube,similarly to the above spiral heater 23. Each of the upper-portionheaters 28 and the lower-portion heaters 26 may have a circular shape, aelliptical shape or a compressed circular shape. The respective shapesof the upper-portion heaters 28 and the lower-portion heaters 26 and therespective numbers of the upper-portion heaters 28 and the lower-portionheaters 26 may be suitably designed based on a thermal calculation inthe reaction container.

According to the embodiment, the temperature control is easy, and theparticle generation can be effectively prevented. In addition, since thelinear wire 4 a has a small thermal capacity, the embodiment is suitablefor rapid heating and rapid cooling, and the embodiment can remarkablyimprove the ununiformity in heating the objects to be processed such assilicon wafers.

(Heating Method)

Hereinafter, a method of conducting a thermal process to silicon wafersas objects to be processed by using the above embodiments is explained.

At first, the whole heating furnace is preliminary heated to a reactiontemperature or vicinity thereof. Then, a plurality of silicon wafers Wto be thermally processed are placed on the object-to-be-processed boat11. The boat 11 is set in the system consisting of the heat-insulatingcylinder 12, the rotational shaft 14, the rotational bearing 15 and theobject-to-be-processed-boat elevating mechanism 16 while the system isunloaded outside the furnace body 1.

Then, the process tube 5 is set over the object-to-be-processed boat 11,and the reaction-container lower lid 10 and the process tube 5 arehermetically sealed to each other via the O-ring (not shown). At thisstage, the gas-discharging pipe 7 has not been connected to thegas-discharging-pipe connecting portion 6 of the process tube 5 yet.

Then, while the upper opening of the furnace body 1 is open, the waferboat 11 covered by the process tube 5 is loaded into a predeterminedposition of the furnace body 1 through the lower portion of the furnacebody 1. Then, the furnace-body lid 2 is set so as to surround thegas-discharging-pipe connecting portion 6 of the process tube 5, whichprotrudes upward from the upper portion of the furnace body 1.Preferably, the furnace-body lid 2 is made of a heat-insulatingmaterial, in order for the heat of the process tube 5 not to dissipatethrough the upper portion thereof.

Then, the flange 17 a at the end portion of the gas-discharging-pipeconnecting portion 6 and the flange 17 b at the end portion of thegas-discharging pipe 7 are connected with each other, and the respectivetemperature controlling units 8 a, 8 b, 8 c, 8 d are arranged for thegas-discharging-pipe connecting portion 6 and the gas-discharging pipe7. Then, a supplier of a fluid for temperature control is connected tothe liquid-flowing tunnel 19 of the flange 17 b. Then, assembly of theunit is completed.

Then, when the heating units 4, 4 a heats the furnace body 1, thetemperatures of the gas-discharging system from the process tube arecontrolled within suitable ranges by means of the temperaturecontrolling units 8 a, 8 b, 8 c, 8 d, while the vacuum pump not showncreates a vacuum in the furnace.

Then, a reaction gas is supplied form a reaction-gas introducing port tostart a reaction (thermal process).

After the reaction is continued for a predetermined time, the supply ofthe reaction gas is stopped. Then, a nitrogen gas is supplied, and thegas remaining in the process tube (the reaction gas and any generatedgas) is discharged. The vacuum pump continues to create a vacuum, butthe heating operation is stopped and the heating furnace is cooled.

According to the above steps, a process to the silicon wafers iscompleted.

In the above embodiments of the invention, the silicon wafer isexplained as an object to be processed. However, the object to beprocessed is not limited to the silicon wafer, but may be a LCDsubstrate or a glass substrate.

EXAMPLE

Hereinafter, a specific example of the invention is explained.

A process tube as shown in FIG. 1 was made of quartz glass.

100 silicon wafers were mounted on a wafer boat made of quartz glass inan alignment, and a silicon nitride film having a thickness of 70 nm wasdeposited on a surface of each silicon wafer at a reaction temperatureof 700° C. by using the process tube and by using a silane-base gas as areaction gas and an ammonium gas. The gas-discharging-pipe connectingportion 6 was heated to 700° C. by means of a carbon wire heater.

As a comparison, a silicon nitride film was formed under the sameconditions, by using a double-tube type of process tube as shown in FIG.4.

As a result, in the example of the invention, it took 200 minutes tocomplete the steps of from preliminary heating to taking-out the siliconwafers. On the other hand, according to the comparison, it took 230minutes.

In addition, in both cases, particle contamination of silicon wafers wasnot generated. Furthermore, in silicon wafers mounted in an upperportion of the wafer boat, there was no phenomenon of ununiformity inheating.

1. A thermal processing unit comprising: a heating-furnace body whose upper end has an opening, a furnace-body lid provided at an opening of the heating-furnace body, a heating unit provided on an inside wall of the heating-furnace body, a reaction container consisting of a single tube contained in the heating-furnace body, a gas-discharging-pipe connecting portion formed at an upper portion of the reaction container and penetrating the furnace-body lid, and a first temperature controlling unit provided around the gas-discharging-pipe connecting portion.
 2. A thermal processing unit according to claim 1, wherein a gas-discharging pipe for discharging atmosphere in the reaction container is connected to the gas-discharging-pipe connecting portion, and a second temperature controlling unit is provided around the gas-discharging pipe.
 3. A thermal processing unit according to claim 2, wherein the first temperature controlling unit and the second temperature controlling unit are adapted to be controlled independently.
 4. A thermal processing unit according to claim 2, wherein a flange is formed at an end portion of the gas-discharging-pipe connecting portion, another flange is formed at an end portion of the gas-discharging pipe, and the flange at the end portion of the gas-discharging-pipe connecting portion and the flange at the end portion of the gas-discharging pipe are hermetically connected via a sealing member.
 5. A thermal processing unit according to claim 4, wherein on at least one of the flange at the end portion of the gas-discharging-pipe connecting portion and the flange at the end portion of the gas-discharging pipe, a third temperature controlling unit for controlling a temperature at a connecting portion of the flanges is provided.
 6. A thermal processing unit according to claim 5, wherein the third temperature controlling unit has a liquid-flowing tunnel formed in the flange.
 7. A thermal processing unit according to claim 5, wherein the third temperature controlling unit has a heating unit for control provided in a vicinity of the flange.
 8. A thermal processing unit according to claim 5, wherein the first temperature controlling unit, the second temperature controlling unit and the third temperature controlling unit are adapted to be controlled independently.
 9. A thermal processing unit according to claim 2, wherein the gas-discharging-pipe connecting portion is bent.
 10. A thermal processing unit according to claim 9, wherein the gas-discharging-pipe connecting portion is bent at an angle of about 90 degrees.
 11. A thermal processing unit according to claim 1, wherein the gas-discharging-pipe connecting portion is formed in such a manner that the gas-discharging-pipe connecting portion is integral with and extended from the reaction container.
 12. A thermal processing unit according to claim 1, wherein the gas-discharging-pipe connecting portion has a cervical portion whose diameter gradually reduces from a diameter at an upper portion of the reaction container.
 13. A thermal processing unit according to claim 12, wherein an assistant heating unit is provided in a vicinity of the cervical portion of the gas-discharging-pipe connecting portion.
 14. A thermal processing unit according to claim 1, wherein the first temperature controlling unit is a heat-insulating member.
 15. A thermal processing unit according to claim 1, wherein the first temperature controlling unit is a resistance heater.
 16. A thermal processing unit according to claim 1, wherein the first temperature controlling unit has a flexibility.
 17. A thermal processing unit according to claim 1, wherein the first temperature controlling unit has been formed into a shape in advance.
 18. A thermal processing method of an object to be processed using a thermal processing unit, the thermal processing unit including: a heating-furnace body whose upper end has an opening, a furnace-body lid provided at an opening of the heating-furnace body, a heating unit provided on an inside wall of the heating-furnace body, a reaction container consisting of a single tube contained in the heating-furnace body, a gas-discharging-pipe connecting portion formed at an upper portion of the reaction container and penetrating the furnace-body lid, a first temperature controlling unit provided around the gas-discharging-pipe connecting portion, and an object-to-be-processed boat arranged in the reaction container, for holding an object to be processed, the thermal processing method comprising: a step of conducting a thermal process of the object to be processed by means of the heating unit, and a step of controlling a temperature of the gas-discharging-pipe connecting portion to a temperature substantially equal to a thermal processing temperature of the object to be processed, by means of the first temperature controlling unit.
 19. A thermal processing method of an object to be processed using a thermal processing unit, the thermal processing unit including: a heating-furnace body whose upper end has an opening, a furnace-body lid provided at an opening of the heating-furnace body, a heating unit provided on an inside wall of the heating-furnace body, a reaction container consisting of a single tube contained in the heating-furnace body, a gas-discharging-pipe connecting portion formed at an upper portion of the reaction container and penetrating the furnace-body lid, an object-to-be-processed boat arranged in the reaction container, for holding an object to be processed, a gas-discharging pipe connected to the gas-discharging-pipe connecting portion, for discharging atmosphere in the reaction container, and a second temperature controlling unit provided around the gas-discharging pipe, the thermal processing method comprising: a step of conducting a thermal process of the object to be processed by means of the heating unit, and a step of controlling a temperature of the gas-discharging pipe to a temperature of 150 to 300° C., by means of the second temperature controlling unit. 